During FYs 2014-15, we have started a project on the relapse fever spirochete, Borrelia hermsii. Since the retirement of Dr. T. Schwan, we have initiated a project to continue his work in understanding the regulation of key virulence factors in B. hermsii. While B. hermsii has the genes encoding the same regulatory proteins as B. burgdorferi (i.e., RpoN, RpoS, RpoD and BosR), the responses of the bacterium to environmental signals, such as temperature, are dramatically different. A hallmark of gene regulation in B. burgdorferi is the RpoN/RpoS regulatory network. This regulatory cascade coordinates the expression of virulence factors required for the successful transmission of B. burgdorferi. However, all strains of relapsing fever spirochetes isolated in North America do not harbor a functional RpoN, suggesting that the RpoN/RpoS regulatory cascade does not exsist in B. hermsii. Therefore, our initial focus has been on developing the necessary biochemical and genetic tools to study the RpoS-, RpoD- and BosR-dependent gene regulation of known virulence factors (i.e., Vmp and Vtp) in B.hersmii.